Muddyjeep810
Seaman Apprentice
- Joined
- Jun 10, 2021
- Messages
- 38
Ok, so I've been digging into this 1977 Johnson 70 Horse motor for a couple weeks now. Quite literally. I've also been researching known issues.
It seems to me the biggest known issue with this motor is the warping exhaust plate. As far as I can tell, that issue occurred in a LOT of Johnson and Evinrude outboards.
I've read tons of threads that mention this issue. So here's my question... Has anybody come up with a fix that actually works? Kind of a backyard engineered solution?
The exhaust plate on mine was quite warped. It was bowed out in the middle, right between the middle and bottom exhaust ports.
Here's what I am going to try... I sanded down the side that was cupped to perfectly flat by focusing on the high ends. It's within 0.03 on my feeler gauge which is good for most cylinder head flatness requirements.
On the opposite side where it was bulged up, I sanded the center down some, but not perfectly flat. The center is still 0.05 or so high.
Here is my rational for that... Most of the bolts securing the two other plates (and the entire exhaust assembly) are around the perimeter, of which one of the plates is a LOT thicker and more stout. By leaving the center of the failure plate just a tad thicker than the perimeter I am hoping to use the perimeter bolts to help hold the center down some, as both of the other two plates are straight.
Either way, it's a fairly cheap, easy experiment. I already drilled two holes in the lower fairing to remove the bottom two bolts. I can have the whole exhaust assembly off in five minutes in the future. I will also be keeping an eye on my plugs and watching for any sign of moisture.
Idk, what do you guys think? Am I delusional? Lol
It seems to me the biggest known issue with this motor is the warping exhaust plate. As far as I can tell, that issue occurred in a LOT of Johnson and Evinrude outboards.
I've read tons of threads that mention this issue. So here's my question... Has anybody come up with a fix that actually works? Kind of a backyard engineered solution?
The exhaust plate on mine was quite warped. It was bowed out in the middle, right between the middle and bottom exhaust ports.
Here's what I am going to try... I sanded down the side that was cupped to perfectly flat by focusing on the high ends. It's within 0.03 on my feeler gauge which is good for most cylinder head flatness requirements.
On the opposite side where it was bulged up, I sanded the center down some, but not perfectly flat. The center is still 0.05 or so high.
Here is my rational for that... Most of the bolts securing the two other plates (and the entire exhaust assembly) are around the perimeter, of which one of the plates is a LOT thicker and more stout. By leaving the center of the failure plate just a tad thicker than the perimeter I am hoping to use the perimeter bolts to help hold the center down some, as both of the other two plates are straight.
Either way, it's a fairly cheap, easy experiment. I already drilled two holes in the lower fairing to remove the bottom two bolts. I can have the whole exhaust assembly off in five minutes in the future. I will also be keeping an eye on my plugs and watching for any sign of moisture.
Idk, what do you guys think? Am I delusional? Lol
